Flat panel display (FPD) technology is one of the fastest growing display technologies in the world, with a potential to surpass and replace cathode ray tubes in the near future. As a result of this growth, a large variety of FPDs exist, such as field effect emission displays (FED), vacuum fluorescent displays (VFD) and thin cathode ray tube displays (CRT), which range from very small virtual reality eye tools to large hang-on-the-wall television displays.
The FPD contains a pair of generally flat glass plates typically rectangular in shape connected together through spacers or side members. The FPD requires a hermetically sealed vacuum envelope formed by sealedly joining the flat plates. The thickness of the relatively flat structure formed with the two plates and the intermediate connecting spacers is much smaller compared to the diagonal length of either plate. In order to provide a vacuumized display one has to bond one glass plate to another leaving a space there between, which space is eventually evacuated.
Basically the flat panel display has two glass sheets bonded to each other about the periphery with the central hollow area containing a vacuum. One or both of the glass plates in certain FPDs may have active components such as TFTs formed thereon and positioned within the hollow of the display.
Thus constructed the glass plates are made of thin glass each having a thickness as small as, for example, about 0.5 to 3.0 mm and are spaced from each other at an interval as small as 0.2 mm, resulting in the envelope being highly reduced in thickness. The typical air evacuation of the envelope is in a range of exceeding 10−7 Torr so that the electrons emit with efficiency. The process to seal and to evacuate gases to insure vacuums exceeding 10−6 Torr level is largely achieved by creating an air tight envelope using heat sources to fuse the side spacers to the anode and the cathode substrates using frit (sealing glass) and then using a pump to evacuate the air. Thereafter, a getter absorbs the balance of residual gas maintaining the envelope at a vacuum equal to or exceeding 10−7 Torr (See for example, Cho, et al U.S. Pat. No. 6,109,994).
Generally the sealing procedure for FPD displays is accomplished by applying a glass frit to the seal area between the support members and the anode substrate and cathode substrate and applying appropriate pressure to the envelope to firmly hold the glass layers that are to be sealed in intimate contact while the entire assembly is subjected to high temperatures in an oven. FIGS. 1a, 1b and 1c are illustrative of the prior art wherein at the assembly point shown in FIG. 1a, spacers such as by way of example spacers 109 and if utilized in certain FPD displays various inner spacer walls 106 are positioned to be mounted on glass anode substrate 160. Frit 102 situates along the lower edges of outer spacer walls 109 that contact substrate 160. The frit 108 situates along outer spacer walls 109 that contact the substrate 110. An evacuation tube (not shown) typically affixes to the backplate of substrate 110 or a side plate member 109 for later evacuation of gases from the sealed FPD.
As illustrated in FIG. 1b substrates 160, 110 and spacers 109 and if utilized spacers 106 are placed in a fixture, jig or alignment system 220 having clamping members 225, and brought into physical contact along frit 102,108, which sit between members 160,110 and member 109. Fixture system 220 is placed in an oven 235. After being aligned and brought into contact along frit 102,108 (FIG. 1a), members 160, 110, 109, and 106 are slowly heated in air to a sealing temperature ranging from 450° C. to greater than 600° C. When the frit 102,108 melts, the oven temperature is then ramped up slowly over a period of 30 minutes to the desired sealing temperature (between 350° C. and 450° C.). The oven 235 holds the temperature constant for approximately 30 minutes. After maintaining the appropriate temperature for the desired time the oven 235 decreases the temperature to ambient over approximately 3 to 4 hours. As the members cool down, composite member 160, 110, 109, and 106 are permanently sealed.
Upon achieving thermal stability at the ambient temperature the FPD is removed from oven 235 and the fixture 220. The pressure in the interior of the FPD is decreased to the desired vacuum level by removing air through the evacuation tube (not shown). The evacuation tube is then closed. FIG. 1c illustrates the final hermetically sealed FPD. The sealing procedure as described produces wasted heat energy, unnecessarily exposes the internal components of the display to high temperatures and is time consuming. These practices reduce the reliability of the display and reduce suitability for mass production.